the star pixel detector - agenda (indico) · 2016-09-05 · extend the measurement capabilities in...

G. Contin | [email protected]

The STAR Pixel detector

Giacomo Contin for the STAR Collaboration Lawrence Berkeley National Laboratory

PIXEL 2016 - 8th International Workshop on Semiconductor Pixel Detectors for Particles and Imaging Sestri Levante, 5-9 September 2016


Outline

A MAPS-based detector Construction Operations, Performance,

Lessons Learned Conclusions

PIXEL2016 - Sestri Levante 2 9/5/2016


SSD r = 22

IST r = 14

PXL r2 = 8

r1 = 2.8

The STAR Heavy Flavor Tracker Extend the measurement capabilities in the heavy flavor domain, good probe to QGP: • Direct topological reconstruction of charm hadrons (e.g. D0 → K π, cτ ∼ 120 µm)

The STAR detector

HFT

@ RHIC

3

200 GeV Au-Au collisions @ RHIC dNch/dη ~ 700 in central events

TPC – Time Projection Chamber (main tracking detector in STAR)

HFT – Heavy Flavor Tracker

SSD – Silicon Strip Detector IST – Intermediate Silicon Tracker PXL – Pixel Detector

σ = ~1 mm

σ = ~300 µm

σ = ~250 µm

σ = <30 µm

Tracking inwards with gradually improved resolution:

R (cm)

Need to resolve displaced vertices in high multiplicity environment


The PiXeL detector (PXL)

PIXEL2016 - Sestri Levante 4

First vertex detector at a collider experiment based on Monolithic Active Pixel Sensor technology

9/5/2016


PXL Design Parameters


DCA Pointing resolution (10 ⊕ 24 GeV/p⋅c) µm

Layers Layer 1 at 2.8 cm radius Layer 2 at 8 cm radius

Pixel size 20.7 µm X 20.7 µm

Hit resolution 3.7 µm (6 µm geometric)

Position stability 5 µm rms (20 µm envelope)

Material budget first layer X/X0 = 0.39% (Al conductor cable)

Number of pixels 356 M

Integration time (affects pileup) 185.6 µs

Radiation environment 20 to 90 kRad / year 2*1011 to 1012 1MeV n eq/cm2

Rapid detector replacement < 1 day

356 M pixels on ~0.16 m2 of Silicon

9/5/2016


Material budget on the inner layer Thinned sensor: 50 µm - 0.068% X0 Aluminum-conductor cable (32 µm-thick traces) - 0.128% X0 Carbon fiber stiffener (125 µm) and sector tube (250 µm) - 0.193% X0 Air cooled

Mechanical support with kinematic mounts (insertion side)

Cantilevered support

PXL System Overview 10 sectors total 5 sectors / half

4 ladders / sector 10 sensors / ladder

carbon fiber sector tubes

Highly parallel system

PIXEL2016 - Sestri Levante 6 9/5/2016

Ladder with 10 MAPS sensors (~ 2×2 cm each)

0.388% X0


PXL MAPS sensor

4 sub-arrays to help with process variation

Digital section End-of-column discriminators Integrated zero suppression (up to 9 hits/row) Ping-pong memory for frame readout (~1500 w) 2 LVDS data outputs @ 160 MHz

Ultimate-2: third MIMOSA-family sensor revision developed for PXL at IPHC, Strasbourg

Monolithic Active Pixel Sensor technology

Pixel matrix 928 rows * 960 columns = ~1M pixel In-pixel amplifier In- pixel Correlated Double Sampling (CDS)


High resistivity p-epi layer Reduced charge collection time Improved radiation hardness

S/N ~ 30 MIP Signal ~ 1000 e- Rolling-shutter readout A row is selected For each column, a pixel is

connected to discriminator Discriminator detects possible hit Move to next row

185.6 µs integration time ~170 mW/cm² power dissipation

9/5/2016


2 m (42 AWG TP)

11 m (24 AWG TP)

100 m (fiber optic)

Highly parallel system 4 ladders per sector 1 Mass Termination Board (MTB) per sector 1 sector per RDO board 10 RDO boards in the PXL system

RDO motherboard w/ Xilinx Virtex-6 FPGA

DAQ PC with fiber link to RDO board

Mass Termination Board (signal buffering) + latch-up protected power

PXL Detector Powering and Readout Chain


Clk, config, data, power

Clk, config, data

PXL built events

Trigger, Slow control, Configuration, etc.

Existing STAR infrastructure

PXL Sector

9/5/2016


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Construction

9/5/2016 PIXEL2016 - Sestri Levante


10 PIXEL2016 - Sestri Levante

PXL Production, Assembly and QA

Production goals: • 2 detector copies • 40 additional spare

ladders for refurbishment • 120 high quality ladders

Production processes: • Sensor probe testing • Ladder assembly • Ladder testing • Sector assembly • Detector-half assembly


PXL Probe Testing Thinned and diced 50 µm-thick sensors Full sensor characterization Full speed readout (160 MHz)

Custom made vacuum chuck Testing up to 18 sensors per batch

(optimized for sensor handling in 9-sensor carrier boxes)

Manual alignment (~1 hr) LabWindows GUI for system control Automated interface to a database

Probe card with readout electronics

Sensors built-in testing functionality Proper probe pin design for

curved thinned sensors Yield 46% - 60% (spare probe cards) Administrative control of sensor ID

curved thinned sensors

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Ladder Assembly

12 PIXEL2016 - Sestri Levante 9/5/2016

Precision vacuum chuck fixtures to position sensors by hand Sensors are positioned with butted edges. Acrylic adhesive prevents CTE difference based damage. Weights taken at all assembly steps to track material and as QA.

Assembled ladder

Cable reference holes for assembly

Hybrid cable with carbon fiber stiffener plate on back in position to glue on sensors.

Sensor positioning

FR-4 Handler


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From ladders to sectors… to detector halves

Metrology picture

Sectors Ladders are glued on carbon fiber sector tubes in 4 steps Pixel positions are measured and related to tooling balls After touch probe measurements, sectors are tested

electrically for damage from metrology

Detector half Sectors are mounted in dovetail slots on

detector half Metrology is done to relate sector tooling

balls to each other and to kinematic mounts

Sector assembly fixture

A detector half

Sector in the metrology setup



PXL Position Control

Position stability Vibration at air cooling full flow: ~5 µm RMS Stable displacement at full air flow: ~30 µm Stable displacement at power on: ~5 µm

Global hit position resolution: ~ 6.2 µm

14 PIXEL2016 - Sestri Levante

Vibration test through capacitive probe

Metrology survey 3D pixel positions on sector (within ~10 µm) are

measured with touch probe and related to tooling balls Sector tooling ball positions related to kinematic

mounts to relate pixel positions to final PXL location

Detector-half is fully mapped

HFT DCA pointing resolution: ( 10 ⊕ 24/p) µm

9/5/2016

Sector in the metrology setup


PXL Installation in STAR


Kinematic mounts Novel insertion approach Inserted along rails and

locked into a kinematic mount inside the support structure

It can be replaced in < 1 day with a spare copy

9/5/2016

duplicate, truncated PXL support tube with kinematic mounts

Insertion in STAR PXL inserted and cabled in STAR


Overall stats #

Assembled ladders 146

Installed on sectors 127

Ladder tests ~2000

-5

0

5

10

15

20

25

30

2013

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- Jan Feb

Mar

Apr

May Jun Jul

Aug Sep

Oct

Nov

Dec

2014

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- Jan Feb

Mar

Apr

May Jun Jul

Aug Sep

Oct

Nov

Dec

2015

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- Jan Feb

Mar

Apr

May Jun Jul

Aug Sep

Oct

Nov

Dec

Ladder and Sector construction Ladders on sector

Ladders assembled

PXL production timeline

Primary Detector construction

Spare Detector construction

Al Inner Ladders + Run14 refurbishment

Run15 refurbishment

Delivered: 2014 Run: Primary Detector, 2 aluminum cable inner ladders, others in copper 2015-2016 Runs: 2 detector copies, all inner ladders in aluminum

Sector refurbishment:

After each STAR Run for latch-up induced damage After power supply accident during 2015 Run installation

9/5/2016 PIXEL2016 - Sestri Levante 16


iWoRID '14 - Trieste 17

Operations, Performance, Lessons Learned

6/23/2014


2013 Engineering Run

Sensor IR picture Flawed ladder dissection: searching for shorts

Inner layer design

PXL Engineering Run assembly crucial to deal with a number of unexpected issues

Limited capability to remotely control power and current limits After the engineering run added functionality to the Mass Termination Board:

remote setting of LU threshold and ladder power supply voltage + current and voltage monitoring

Shorts between power and gnd, or LVDS outputs

Adhesive layer extended in both dimensions to increase the portion coming out from underneath the sensors

Insulating solder mask added to low mass cables

Mechanical interference in the driver boards on the existing design.

The sector tube and inner ladder driver board have been redesigned to give a reasonable clearance fit

Inner layer design modification: ~ 2.8 cm inner radius

Engineering run geometry



PXL data taking Timeline:

PXL Operations

Hit multiplicity per sensor: up to 1000/inner-sensor, 100/outer-sensor Dead time up to ~6% Typical trigger rate: 0.8-1 kHz Latch-up reset events: 2 latch-up/min Periodic reset to clear SEUs

Collected minimum bias events in the PXL acceptance:

2014 Run: ~ 1.2 Billion Au+Au @ √sNN = 200GeV

2015 Run: @ √sNN = 200GeV

2016 Run: @ √sNN = 200GeV

~ 1 Billion p+p ~ 0.6 Billion p+Au ~ 2 Billion Au+Au ~ 0.3 Billion d+Au


2013 2014 2015 2016

2014-2016: HFT data taking PXL Engineering Run HFT decommissioned

PXL R&D

~ 2003


Operational issues: Latch-up damage

Unexpected damage seen on 15 ladders in the STAR radiation environment in 2014 Run first 2 weeks Digital power current increase Sensor data corruption Hotspots in sensor digital section Correlated with latch-up events Limited with operational methods

Latch-up tests at BASE facility (LBL) to measure latch-up

cross-section and reproduce damage 50 µm & 700 µm thick, low and high resistivity sensors; PXL ladders Irradiation with heavy-ions and protons

Results and observations

Current limited latch-up states observed (typically ~300 mA) Damage reproduced only with HI on PXL 50 µm thinned sensors

Safe operations envelope implemented

Latch-up protection at 80 mA above operating current Periodic detector reset to clear SEU

Latch-up phenomenon: • Self feeding short circuit

caused by single event upset • Can only be stopped by

removing the power

Inner layer damage: 14%


Operating current evolution. Threshold is set at ~1.2A here

9/5/2016


Latch-up test setup and damage analysis


Individual sensor test boards and ladders mounted on cooling plate

6 hot spots this location 5 hot spots this location

IR “hotspots” locating the damage tend to favor particular structures (isolated buffers with specific structure pitch)

Pixel sensor layers deconstructed (plasma etching technique) and viewed with SEM. The layers appear to be melted

1 µm

9/5/2016


Damage evolution


Run Good sensors on Inner Layer

Good sensors on Outer Layer Comment

installation end of run installation end of run

2014 100% 82% 100% 95% LU damage, most of it in the first 15 days of operations

2015 99% 94% 98% 96% (93%)* * = Lost control of an outer ladder (10 good sensors off)

2016 100% 95% (87%)+ 99% 98% + = Current instability on inner ladder (8 good sensors off)

9/5/2016

Good sensor = sensor with >95% active channels and uniform efficiency

2014 2015 2016


DCA pointing resolution Design requirement exceeded: 46 µm for 750 MeV/c

Kaons for the 2 sectors equipped with aluminum cables on inner layer

~ 30 µm for p > 1 GeV/c

From 2015: all sectors equipped with aluminum cables on the inner layer

Physics of D-meson productions High significance signal Nuclear modification factor RAA

Collective flow v2

HFT Performance from 2014 data


D0 → K π production in √sNN = 200GeV Au+Au collisions (First reconstruction of a small subsample)

46 µm

9/5/2016


Software/Firmware issues


Event decoder issue in 2014 data reconstruction A bug in the PXL hit decoding software led to an efficiency loss in the reconstructed

2014 Run data, affecting the preliminary STAR results

Readout firmware issue - 2015 efficiency loss A subtle bug introduced by a change in the PXL RDO firmware led to an efficiency

loss in the 2015 Run data The extensive tests with pattern data and the performance of full detector calibrations

were inadequate to find this problem A fast-offline tracking QA was put in place only after the 2015 Run A post-run investigation based on external sensor illumination with LED allowed for

firmware debugging and correction

After fixing the bug, the new data reconstruction and analysis showed a significant improvement in the performance, which now matches the simulation

data - simulation comparison

D0 → K π significance improvement


Conclusions


The first generation MAPS-based detector at a collider experiment successfully completed the 3-year physics program at RHIC

As part of the Heavy Flavor Tracker, the PXL detector enabled STAR to perform a direct topological reconstruction of the charmed hadrons

The 2013 Engineering Run was crucial for dealing with the unexpected problems that developed during the following physics data taking

Due to beam-induced damage, the PXL construction phase continued throughout the entire detector life for yearly refurbishment and optimization

The relatively short duration of the HFT program is not optimal to exploit such a complex detector system, nevertheless the project was successfully completed


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the star pixel detector - agenda (indico) · 2016-09-05 · extend the measurement capabilities in...

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